Pristinamycin II.sub.B derivatives have been described previously in American Patents U.S. Pat. No. 4,590,004 and U.S. Pat. No. 4,668,669. These products have the property of synergizing the antimicrobial activity of pristinamycin I.sub.A.
Vinyl sulphones are useful products as synthesis intermediates, especially in carrying out Michael reactions. Their preparation is generally performed in several steps, among which an oxidation step and often the isolation of an intermediate sulphone take place, since the preparation is performed in most cases by proceeding via a thiol.